Begin by cutting the zucchini and yellow summer squash into 1-inch thick rounds or chunks. Slice the red onion into thick wedges, ensuring the root end remains intact.

Pat the cut vegetables aggressively with paper towels to remove any surface moisture.

Heat a heavy-bottomed cast-iron grill pan over medium-high heat until it begins to shimmer.

In a large bowl, combine the dried vegetables with oil, garlic powder, and smoked paprika. Toss until coated.

Place the seasoned zucchini and squash into the preheated pan in a single layer. Cook undisturbed for about 4 minutes.

After 4 minutes, add the onion wedges to the pan, flipping all vegetables over. Cook for an additional 3 minutes.

Once cooked, remove the vegetables from the pan and transfer them to a serving dish. Sprinkle with salt and drizzle with balsamic glaze.